Shower base



FIG. 1 is a front perspective view of a shower base showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a side view thereof;

FIG. 5 is a side view of the opposite side of FIG. 4; and,

FIG. 6 is a top view thereof.

The broken lines shown in the drawings illustrate portions of a shower base that form no part of the claimed design. 

CLAIM I claim the ornamental design for a shower base, as shown and described. 